When using the parametric hex-dominant meshing tool without running a volume extraction operation beforehand, you have to click on this button after the mesh is finished:
Your mesh had some issues. The aspect ratio of your cells could be better. You want values close to 1 (cubic cells):
Extending the domain a little bit is also a good idea, to give some room for the flow to settle.
To save you some trouble, I drafted one mesh to get you started, which you can find in this link https://www.simscale.com/workbench/?pid=63269172894931018&mi=spec%3A7c4cfc6c-f166-471b-be3a-30e881f07c47%2Cservice%3AMESHING%2Cstrategy%3A16&sh=1
There’s definitely things I encourage you to play with, like domain size, bounding box resolution, refinements etc.
In this project you will also find a converged run using the draft mesh. I chose to use a combination of velocity inlet and a custom outlet BC but there should be other combinations possible (and more representative than this one even).